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I'm considering purchasing a digital piano at some point soon, and what I'm interested in is what the different methods of measuring and interpreting velocity are, and how that translates to MIDI.

My initial thought is that, for realisms sake, the two systems must be different, with MIDI being an approximation of the true velocity. MIDI only has 127 possible values for velocity (at least on the standard channel, 7 is it, I can't remember). Yet that would be extremely limiting for a good quality digital piano which would need many more velocity values than 127?

So, for live playing etc. does the digital piano use a much wider range of values for velocity, but when outputting via MIDI, just maps those to a much smaller range?

It doesn't make much difference overall, because a lot of my usage will be live performance, but I'm interested to know how it works.

Hmmm....Your question covers very broad area of discussions.Search this forum for more info on velocity.There is no standard among digitals for measuring velocity. If you hit a key moderately hard, one digital may transmit 90 while another may transmit 110. The resulted sound is the same because the sound engine of each digitals is calibrated to a sound very close to the one produced on real piano with given strike force.It is the sound engine that make the digital piano sound. Velocity number is just a number. Does not have real meaning. Velocity use number 0~127 because it is based on digital system(hexa decimal numbers)protocol.But... If you connect 2 different digital models(e.g.digital piano connected with synthesizer), it could be an issue. In that case, you need to calibrate the machine that make the sound appropriately. Or, you will have unusual sounding digital piano sound(too extreme in volume for given key strike force).

I didn't think that internally a (good) digital piano would simply stick to 128 different velocity measurements - there must be thousands. So when it translates it to a MIDI velocity for purpose of output, it just approximates?

I would therefore get a better expressive range (all else being equal) using an 'all-in-one' digital piano than using a weighted master MIDI keyboard and a sound module, because MIDI sacrifices velocity info?

Actually, I don't think the digital piano exists that utilizes all of midi's 128 velocity levels for discrete samples. Which would correspond at a minimum to 128 recordings for the pedal up and another 128 for the pedal down. For each key. The largest sampled piano I've seen is Sampletekk's TBO which I believe does 31 pedal-up, 31 pedal-down, and 31 release samples per note. 16 samples all around is otherwise considered pretty good in hard-disk sample libraries. The best hardware digital pianos, however, typically only do 1 to 4 pedal-up samples and simulate the pedal-down's with reverb. The cheaper hardware units might just do 1 sample per octave and derive the other notes by pitch shifting.

That's not to say that any of the above can't put out 128 different volume levels for each note. They just do it by scaling the volumes of the samples they got to fill in the blanks.

Yamaha has created something called high-definition MIDI for their Disklavier Pro series of pianos to deal with just this issue. The inherent limitation of dealing with only 128 possible values for velocity was the primary reason.

The high resolution Disclavier technique is licensed to Yamaha by Wayne Stahnke who developed it in 1983. I don't think Yamaha implements the full Stahnke sevo-control system, however, due to its expense and bulk. The full system was originally implemented by Bosendorfer in their 290 SE-series of which I belive only 37 were ever manufactured. In addition, I'm aware of the existence one 1923 Steinway Model D which Stahnke probably did by private commission.

Oops.... There is no real 32 velocity level recorded digital piano samples.. so forget it. I understand those software pianos are advertised as 16 velocity levels..etc.. In reality, all they have is 6 velocity pedal up and pedal down plus noises samples. I have some of those giga software pianos. The sound is processed in response to 16 different velocity level and that is what it really is.Going back to original question...Digital pianos use audio samples(audio files). These samples are recorded from real piano played at different "velocity". If you listen to real piano sound carefully, changes in tone quality happen in very subtle manner when keys are stiken at different velocity. It depends on different real piano models too. Only 5 or 6 different strike forces(ppp, pp, p, mf, f, ff )makes notable different quality tones. In between, just a matter of loudness. Try this with your real piano if you have one. Digitals are based on this finding. So, 128 velocity value is more than enough to represent real piano. No one can even create 32 different velocity piano sound that is differ in quality yet. So... forget any velocity value above 127.

... " Digital pianos use audio samples(audio files). These samples are recorded from real piano played at different "velocity". If you listen to real piano sound carefully, changes in tone quality happen in very subtle manner when keys are stiken at different velocity. It depends on different real piano models too. Only 5 or 6 different strike forces(ppp, pp, p, mf, f, ff )makes notable different quality tones. In between, just a matter of loudness. Try this with your real piano if you have one. Digitals are based on this finding ". ......

This is spot on DKPCOLA. People who are trying to understand their digital pianos should take note of that.

Most digital piano sounds these days are derived from 2, 3 or 4 'layers'.

Here is an example ... "Superior Grand" patch on Roland RD700sx.

Roland have recorded samples of all 88 keys struck at 4 different velocities. (Just for reference they call these strikes 'p', 'mp', 'f' and 'ff').

These samples are then processed by the engineer/tech guys ... they 'assemble' the 4 layers of each note to produce a note that has 4 different tones to it depending on how hard it is struck.

The 4 velocity 'ranges' on the "Superior Grand" patch are as follows ..... 2-40, 41-69, 70-110 and 111-127.

If you play a note with a velocity of say 50, you will hear the sound/tone of the 2nd layer. If you strike a note rather forcefully e.g. a velocity of around 120, you will hear the very bright sound/tone of the 4th layer (range 111-127).

Bear in mind that this is a very simple explanation. (the recorded samples are also in stereo and I have not mentioned samples with the damper pedal depressed among other things).

Also just BTW, when a manufacturer says that their piano sound is for example, a "3 layered" one, they are *not* counting the sustain sample.

Andy .... in reply to your original question .... I'm almost certain that when a note is struck on a digital piano, a velocity value of 1-127 is sent to the pianos internal 'workings' just the same as what is sent to the 'midi out'.

Hope this is helpful and interesting in some way. Regards, Charles :-)

p.s. ... if Dave McMahan from General Music is about he may ... 1. comment on the accuracy of this post and ... 2. comment on the disadvantages of this 'layered' approach to acheiving a piano sound. (GEM use a different system altogether to get their fantastic piano sounds).